Preparation of buta-1,3-diynyl complexes of platinum(II) and their use in the construction of neutral molecular squares:: synthesis, structural and theoretical characterisation of cyclo-{Pt(μ-CCCC)(dppe)}4 and related chemistry

Copper(I)-catalysed reactions of cis-PtCl2(L)(2) (L= PEt3, L-2 = dppe, dppp) with buta-1,3-diyne have given the corresponding diynyl complexes, cis-Pt(C=CC=CH)(2)(L)(2) (L = PEt3 1, L-2 = dppe 2, dppp 3) whose solid-state structures have been determined from single crystal X-ray diffraction studies. Theoretical calculations were carried out to probe the electronic structure of these diynyl complexes. Complex 2 reacts with Co-2(CO)(8) to give a bis-adduct 5 and with Ru-3(mu-dppm)(CO)(10) to give a mono-adduct 6; in both, the least hindered C=C triple bond(s) is(are) coordinated. Lithiation (LiBut) of 2 gives a dilithio derivative, which has been converted to dimethyl 7 or mono-SiMe3 8 or -Au(PPh3) 9 complexes. Cu(I) and Ag(I) (M-I) adducts ("tweezer" complexes) have been obtained from reactions of 2 with (MSCN)-S-I or [M-I(NCMe)(4)](+). An ES mass spectrometric study of the interactions of 2 with Group 1 cations and with Tl+ is also described; comparative experiments with {W(CO)(3)Cp}(2)(mu-C-8), in which the four C=C triple bonds do not have a "tweezer" conformation, have also been carried out. The degree of association is determined by the competitive solvation of the Group 1 cation. Coupling of the buta-1,3-diynyl complexes with Pt(OTf)(2)(L')(2) gives homo- or mixed-ligand molecular squares cyclo-{(L)(2)Pt(mu-C=CC=C)(2)Pt(L')(2)}(2) (L, L' = PEt3, L-2, L'(2) = dppe, dppp; not all combinations), of which the molecular structure of cyclo-{Pt(mu-C=CC=C)(dppe)}(4) 17 is described (as solvates containing dmso). The molecular squares form adducts with substituted ammonium triflates [NH2R2][OTf] (R = Et, Pr-i, Cy; NH2R2 = dbuH) and with Group 11 cations [M-I(NCMe)](+).